P4 - Atomic Structure

Question 1

What happens to an electron in an atom if it releases EM radiation?

Answer 1

If they release EM radiation, they move to a lower energy level closer to the nucleus.

And if they absorb EM radiation, they move to a higher energy level and move further away from the nucleus.

Question 2

What is the radius of an atom?

Answer 2

The radius of an atom is about 1 x 10^-10 m.

Question 3

What is the atomic number of an atom?

Answer 3

The atomic number = number of protons

Question 4

What is the mass number of an atom?

Answer 4

Mass number = number of protons + number of neutrons.

Question 5

What is an isotope?

Answer 5

Isotopes are variants of a particular element which have a different number of neutrons.

Question 6

What is radioactive decay?

Answer 6

When an isotope is unstable, they tend to decay into other elements and give out radiation as they try to become more stable (they tend to try to balance protons and neutrons or get rid of excess energy) - this process is called radioactive decay.

Question 7

What is ionising radiation?

Answer 7

Ionising radiation is radiation that knocks off atoms, creating positive ions. The three types are called alpha, beta and gamma.

Question 8

Give three charcteristics of an alpha particle.

Answer 8

An alpha particle is two neutrons and two protons, they don’t penetrate very far into materials and are strongly ionising.

Question 9

Give three characteristics of a beta particle?

Answer 9

A beta particle is a fast-moving electron, it is moderately penetrating and moderately ionising.

Question 10

Give three characteristics of a gamma ray?

Answer 10

Gamma rays are waves of electromagnetic radiation, they penetrate far into materials but are weakly ionising.

Question 11

In nucleur equations, what form are they written in?

Answer 11

Atom before decay → atom after decay + radiation emitted.

Question 12

What is the one golden rule to remember for nucleur equations?

Answer 12

The total mass and atomic numbers must be equal on both sides.

Question 13

Here is an example of alpha decay;

Answer 13

Uranium₉₂²³⁸ → Thorium₉₀²³⁴ + He₂⁴

(As you can see; the atomic number and mass number are the same on both sides)

Question 14

So when an alpha decay occurs, what happens?

Answer 14

The atom’s atomic number reduces by 2, and its mass number reduces by 4.

Question 15

What hapens when beta decay occurs?

Answer 15

A neutron turns into a proton and releases a fst-moving electron. So the mass number does not chnage however the proton number decreases by 1.

Question 16

What happens when gamma rays occur?

Answer 16

Gamma rays are a way of getting rid of excess energy - so there is no change to the mass or atomic number.

Question 17

What is half-life?

Answer 17

The half-life is the time taken for the number of radiactive nuclei in an isotope to halve.

Question 18

What is irradiation?

Answer 18

Irradiation is the exposure to radiation.

Question 19

What is contamination?

Answer 19

Contamination is radioactive particles getting onto objects.

Question 20

How does a smoke detector work?

Answer 20

A radioactive material fires alpha particles at a smoke detector.

If there is smoke between the smoke detector and the radioactive material, then fewer alpha particles will reach the smoke detector. Therefore, this will set off the smoke alarm.